1. Field of the Invention
The present invention relates in general to a fluid-filled active vibration damping device which actively damps the vibration of an object by controlling the pressure of non-compressible fluid filling a pressure receiving chamber of the damping device, and in particular to such a fluid-filled active vibration damping device which is suitably used as an engine mount or a vibration damper in an automotive vehicle.
2. Related Art Statement
For damping vibration (including noise due to the vibration) of an object to be damped, such as the body or other members of an automotive vehicle that are subject to vibration, there have been various vibration damping devices such as a vibration damping connector and a vibration damper. The vibration damping connector, such as an engine mount, is interposed between a vibration source and an object whose vibration is to be damped, in order to damp the vibration to be transmitted from the vibration source to the object. The vibration damper, such as a dynamic damper, is attached directly to the object to absorb or damp the vibration of the object.
In this background, there has been proposed a fluid-filled active vibration damping device, as an example of such a vibration damping device as described above, as disclosed in Japanese Patent Applications TOKU-KAI-HEI No. 2-42228 and No. 9-49541 and Japanese Patents No. 2510914 and No. 2510925. Such a fluid-filled active vibration damping device includes (a) an elastic body which is elastically deformed when a vibration is input to the damping device and which partially defines a pressure receiving chamber filled with a non-compressible fluid; (b) an oscillating body which partially defines the pressure receiving chamber; and (c) a drive device which oscillates the oscillating body, so as to control a pressure of the non-compressible fluid in the pressure receiving chamber. In this vibration damping device, the pressure of the non-compressible fluid in the pressure receiving chamber is so controlled as to adjust the vibration damping characteristics of the damping device and thereby exhibit an active vibration damping effect, or to generate a controlled oscillating force and thereby actively damp the vibration of an object.
Meanwhile, in the vibration damping device constructed as described above, it is required that an output member of the drive be connected to the oscillating body, in order to transmit the output force of the drive device to the oscillating body. To this end, it has conventionally been practiced, as disclosed in the above-indicated publications, that the output member of the drive device is directly fixed to the oscillating body with a bolt, by press-fitting, or by caulking.
However, each of the above-indicated fixing methods has the problem that to fix the output member to the oscillating body is cumbersome, and accordingly is not suitable for the mass production of vibration damping devices. In addition, when the output member is fixed to the oscillating body, external forces are applied to the oscillating body, so that a large deformation may be produced in the oscillating body or a large strain may be left in the same. This problem leads to decreasing the life expectancy of those elements or lowering the accuracy of assembling of the same. Moreover, the defective assembling of the output member and the oscillating body leads to unstable accuracy of the products, which in turn leads to unstable performance of the same. Furthermore, the above-indicated fixing methods cannot assure that the output member remains fixed to the oscillating body with a sufficiently great strength for a long period of use.
For example, the bolt-using fixing method has the problem that it needs the technique and control to maintain a constant bolt-fastening torque and, in some cases, needs a mechanism for locking a bolt-loosening preventing screw, and the problem that to screw the bolt is cumbersome and time-consuming. The press-fitting fixing method has the problem that it needs a high accuracy of control of dimensions of the elements, in order to obtain stably sufficiently great fixing strength and reliability, and the problem that each element needs a sufficiently great strength to stand the load applied thereto upon press-fitting. The caulking fixing method has the problem that it needs a large-size caulking device and the problem that each element needs a sufficiently great strength to stand the load applied thereto upon caulking. In each of the above-indicated fixing methods, external forces, such as screwing force or press-fitting force, are inevitably applied to the oscillating body and accordingly strains are left in the same, so that the accuracy of dimensions of the oscillating body and the life expectancy of the same may be lowered.
There is also known a vibration damping device which additionally includes (d) a flexible diaphragm which partially defines an equilibrium chamber which is provided on one of both sides of the oscillating body that is opposite to the other side thereof on which the pressure receiving chamber is provided, the equilibrium chamber being filled with the non-compressible fluid, a volume of the equilibrium chamber being changed by deformation of the flexible diaphragm; and (e) an orifice for fluid communication between the pressure receiving chamber and the equilibrium chamber. This damping device additionally exhibits a passive vibration damping effect based on the resonance of the fluid flowing through the orifice. In this case, since, the pressure receiving chamber and the equilibrium chamber, each filled with the non-compressible fluid, are provided on both sides of the oscillating body, respectively, it is very difficult to fix directly the output member of the drive device to the oscillating body, in view of not only the structure of the damping device but also the fixing operation itself.
It is therefore an object of the present invention to provide a fluid-filled active vibration damping device including a novel drive-force transmitting structure which can transmit, with high durability and reliability, a drive force of a drive device to an oscillating body, and which can be simply constructed and assembled.
To this end, the present invention provides a fluid-filled active vibration damping device which has one or more of the technical features that are described below in respective paragraphs given parenthesized sequential numbers (1) to (8). Any technical feature which includes another feature shall do so by referring, at the beginning, to the parenthesized sequential number given to that feature. Thus, two or more of the following technical features may be combined, if appropriate. Each technical feature may be accompanied by a supplemental explanation, as needed. However, the following technical features and the appropriate combinations thereof are just examples to which the present invention is by no means limited. Rather, the concept of the present invention should be understood based on the entire description of the specification and the entire illustration of the drawings.
(1) According to a first feature of the present invention, there is provided a fluid-filled active vibration damping device, comprising an elastic body which is elastically deformed when a vibration is input to the damping device and which partially defines a pressure receiving chamber as a portion of a fluid chamber filled with a non-compressible fluid; an oscillating body which partially defines the pressure receiving chamber; a drive device which oscillates the oscillating body, so as to control a pressure of the non-compressible fluid in the pressure receiving chamber, the drive device comprising an output member which is formed independent of the oscillating body and which is movable in a direction of oscillation of the oscillating body; a first biasing device which biases the oscillating body toward the output member of the drive device; and a second biasing device which biases the output member of the drive device toward an outside surface of the oscillating body, so that the output member is held in direct or indirect contact with the outside surface of the oscillating body.
In the fluid-filled active vibration damping device according to the first feature (1) of the present invention, the output member of the drive device is formed independent of the oscillating body which partially defines the pressure receiving chamber as a portion of the fluid chamber, and the output member and the oscillating body can be held in pressed contact with each other by the respective biasing forces of the first and second biasing devices, in the direction of oscillation of the oscillating body. When the output member is displaced toward, or away from, the oscillating body by the drive force of the drive device, the output member is maintained in pressed contact with the oscillating body, owing to the drive force of the drive device and the biasing force of the first biasing device, or the biasing force of the second biasing device, so that the drive force of the drive device can be stably transmitted to the oscillating body in the direction in which the oscillating body is pushed and drawn.
Thus, it is not needed to fix the output member to the oscillating body with a bolt, by press-fitting, or by caulking. Rather, the output member and the oscillating body can be assembled in the state in which the two elements are just in contact with each other. Therefore, the present damping device can enjoy a simple construction, and can be easily assembled and accordingly be mass-produced. Since no physical fixing means such as a bolt, press-fitting, or caulking is interposed between the output member and the oscillating body, external forces applied to the oscillating body when the output member and the oscillating body are assembled can be minimized or even zeroed. Thus, substantial fixing of the output member and the oscillating body can be achieved with high durability and reliability, and the drive force of the drive device can be stably transmitted to the oscillating body.
In the present damping device, the first and second biasing devices apply the respective biasing forces to the oscillating body and the output member in the opposite directions, respectively. Therefore, at a neutral position of the oscillating body where no drive force is applied thereto from the output member, the respective biasing forces of the two biasing devices can be prevented from being directly applied to the oscillating body or a drive-force generating device of the drive device. Thus, at the neutral position, the respective biasing forces of the two biasing devices can be prevented from acting as significant external forces on the oscillating body, and accordingly the problems that the oscillating body is deformed and the life expectancy thereof is lowered are avoided. In addition, the output force of the drive device that is needed to displace the oscillating body away from its neutral position, can be decreased, which contributes to improving the energy efficiency of the present damping device.
In addition, since the first and second biasing devices apply the respective biasing forces to the oscillating body and the output member in the opposite directions, respectively, a restoring force is effectively generated which restores the oscillating body to its neutral position. Accordingly, for example, the drive device may be either of a double-acting type, or of a single-acting type wherein a drive force is exhibited in one direction only. In each case, the output member and the oscillating body are advantageously held in pressed contact with each other, owing to the respective biasing forces of the first and second biasing devices, so that the present damping device can operate in a stable manner.
The drive device is just required to have the output member which can apply, to the oscillating body, a drive force having a desired frequency. Accordingly, for example, the drive device may be provided by an electromagnetic actuator which utilizes an electromagnetic force, or a pneumatic actuator which utilizes an air pressure. The oscillating body is just required to be displaceable by the drive device. For example, the oscillating body may be provided by an elastic plate member which is displaceable by elastic deformation thereof, a hard plate member which is allowed to displace over a predetermined stroke, or a complex body which includes a hard displaceable member and an elastically deformable, annular support member which surrounds the displaceable member and which causes, when being elastically deformed, the displacement of the displaceable member. The first and second biasing devices are just required to bias the oscillating body and the output member in the opposite directions, respectively, in which the two elements are brought into contact with each other. For example, each of the two biasing devices may be provided by a coil spring, a biasing rubber member, or a leaf spring. The second biasing device may be provided as an integral portion of the drive device. The output member of the drive device may be held in direct contact with the oscillating body, or held in indirect contact with the body via a third member such as a flexible diaphragm which will be described later.
In short, in the present damping device, the output member of the drive device is held in contact with the oscillating body, owing to the respective biasing forces of the first and second biasing devices, so that the drive force of the drive device is transmitted from the output member to the oscillating body and accordingly the oscillating body is displaced or oscillated. Therefore, it is not needed to fix physically the output member of the drive device to the oscillating body. Accordingly, the output member and the oscillating body are easily assembled and, when the two elements are assembled, no significant forces are exerted to the oscillating body, which contributes to improving the durability of the oscillating body. In addition, the present damping device is free from the problem that the accuracy of dimensions of the product is lowered because of the defective assembling of the output member and the oscillating body, and the problem that the stability of operation of the product is lowered because of coming of the output member off the oscillating body. Thus, the present damping device can enjoy much improved life expectancy and reliability.
(2) According to a second feature of the present invention that includes the first feature (1), the oscillating body comprises a hard displaceable member which is provided in a central portion thereof with which the output member of the drive device is held in contact; and an elastically deformable, annular support member which is provided around the displaceable member and which allows, when being elastically deformed, the displaceable member to be displaced.
In this vibration damping device, the central portion of the oscillating body is defined by the hard displaceable member, and the output member of the drive device is held in pressed contact with the hard displaceable member. Therefore, the pressed contact of the output member with the oscillating body can be maintained in a more stable manner.
(3) According to a third feature of the present invention that includes the first or second feature (1) or (2), the fluid-filled active vibration damping device further comprises an inside press member which has a planar contact surface held in contact with an inside surface of the oscillating body; and an outside press member which is provided integrally with the output member of the drive device and which has a planar contact surface held in contact with the outside surface of the oscillating body, and the first biasing device indirectly biases the oscillating body via the inside press member and the second biasing device indirectly biases the output member via the outside press member.
In the present damping device, the respective biasing forces of the first and second biasing devices are transmitted to the oscillating body and the output member, respectively, in a more stable manner via the respective planar contact surfaces of the inside and outside pressure members. In addition, since the respective biasing forces of the first and second biasing devices act on the oscillating body and the output member, respectively, over respective wide areas via the respective planar contact surfaces of the inside and outside pressure members, the present damping device is prevented from unstable operation because of local transmission of the respective biasing forces to the oscillating body and the output member. Rather, respective great biasing forces are stably transmitted to the two elements. Moreover, since a portion of the oscillating body that corresponds to the inside and outside press members is prevented from deformation, by the two press members, the oscillating body may be provided by an elastic plate member which, however, does not have a hard displaceable member in a central portion thereof. In the last case, too, the pressed contact of the output member with the oscillating body can be stably maintained, which leads to improving the stability of operation of the damping device and the durability of the same.
(4) According to a fourth feature of the present invention that includes any one of the first to third features (1) to (3), the pressure receiving chamber comprises a primary chamber in which the pressure of the non-compressible fluid is directly changed when the elastic body is elastically deformed; and an auxiliary chamber in which the pressure of the non-compressible fluid is directly changed when the oscillating body is oscillated, and the damping device further comprises means for defining a first orifice for fluid communication between the primary chamber and the auxiliary chamber, so that a change of the pressure of the non-compressible fluid in the auxiliary chamber that is caused by the oscillation of the oscillating body is transmitted to the non-compressible fluid in the primary chamber via the first orifice.
In this damping device, the change of pressure of the non-compressible fluid in the auxiliary chamber, caused by the displacement of the oscillating body, can be efficiently transmitted to the primary chamber, by utilizing the resonance of the fluid flowing through the first orifice. That is, the small oscillating force applied to the oscillating body can be utilized to control the pressure of the non-compressible fluid in the large primary chamber and thereby obtain an active vibration damping effect. In addition, if the structure and shape of the auxiliary chamber are appropriately selected, a wall defining the auxiliary chamber can be utilized to provide, in the auxiliary chamber, the first biasing device, such as a coil spring, which bridges between the wall and the oscillating body.
(5) According to a fifth feature of the present invention that includes any one of the first to fourth features (1) to (4), the fluid-filled active vibration damping device further comprises a flexible diaphragm which partially defines an equilibrium chamber which is provided on one of both sides of the oscillating body that is opposite to the other side thereof on which the pressure receiving chamber is provided, the equilibrium chamber being filled with the non-compressible fluid, a volume of the equilibrium chamber being changed by deformation of the flexible diaphragm, the pressure receiving chamber and the equilibrium chamber cooperating with each other to provide the fluid chamber; and means for defining a second orifice for fluid communication between the pressure receiving chamber and the equilibrium chamber, and the output member of the drive device is formed independent of the oscillating body and the flexible diaphragm and is held in indirect contact with the outside surface of the oscillating body via the flexible diaphragm.
When a vibration is input to this damping device, the elastic body is elastically deformed and the pressure of the non-compressible fluid in the pressure receiving chamber is changed, so that a pressure difference is produced between the pressure receiving chamber and the equilibrium chamber and the fluid flows through the second orifice. The present damping device can exhibit a passive vibration damping effect based on the fluid flowing through the second orifice, e.g., the resonance of the fluid. In particular, in the case where the passive vibration damping effect based on the fluid flowing through the second orifice is tuned to, and exhibited at, a lower frequency range than that to which and at which the active vibration damping effect based on the oscillation of the oscillating body is tuned and exhibited, the damping device can advantageously exhibit both of the passive and active vibration damping effects. In addition, since the equilibrium chamber is provided on the other side of the oscillating body that is opposite to the one side thereof on which the pressure receiving chamber is provided, it can easily form the equilibrium chamber in a wide space and with a great volume. Moreover, since the output member of the drive device is formed independent of the oscillating body and the flexible diaphragm, and is held in contact with the oscillating body via a flexible diaphragm, it is not needed to hold the output member in contact with the oscillating body such that the output member extends through the diaphragm. Thus, the present damping device can enjoy a simple construction. Furthermore, since it is not needed to assemble the output member of the drive device and the oscillating body in a mass of the non-compressible fluid, the present device can be manufactured with a high efficiency. In addition, since the output member is formed independent of the flexible diaphragm that partially defines the equilibrium chamber, the diaphragm is not subjected to any significant external forces when the output member is assembled with other members of the damping device. Thus, the durability of the diaphragm is improved.
(6) According to a sixth feature of the present invention that includes the fifth feature (5), the oscillating body comprises a hard displaceable member which is provided in a central portion thereof with which the output member of the drive device is held in contact; and an elastically deformable, annular support member which is provided around the displaceable member and which allows, when being elastically deformed, the displaceable member to be displaced, and the flexible diaphragm comprises a hard connecting member which is provided in a central portion thereof sandwiched by, and between, the displaceable member of the oscillating body and the output member of the drive device and which is fixed to the displaceable member.
In this damping device, the oscillating body and the diaphragm are prevented from being displaced relative to each other, and accordingly defective transmission of the oscillating force to the oscillating member because of, e.g., out-of-position movement of the diaphragm, or wrinkle of the same is avoided. In addition, the diaphragm is freed of the problem that the durability thereof is lowered by friction-caused wearing thereof.
(7) According to a seventh feature of the present invention that includes any one of the first to sixth features (1) to (6), the fluid-filled active vibration damping device further comprises a first mounting member and a second mounting member which are elastically connected to each other by the elastic body, the oscillating body is supported by the second mounting member such that the oscillating body is displaceable, and the drive device is supported by the second mounting member, and one of the first and second mounting members is fixed to an object whose vibration is to be damped by the damping device.
The present fluid-filled active vibration damping device can enjoy a simple construction. In particular, in the case where the first mounting member is fixed to one of a vibration transmitting member (e.g., a vibration generating member) and a vibration receiving member (i.e., an object whose vibration is to be damped or prevented) and the second mounting member is fixed to the other member, the present damping device advantageously provides a vibration damping connector, e.g., an engine mount. In addition, in the case where one of the first and second mounting members is fixed to an object whose vibration is to be damped or prevented, so that the other member is elastically supported on the object via the elastic body and thus a vibration system is provided, the present damping device advantageously provides a vibration damper.
(8) According to an eighth feature of the present invention that includes any one of the first to seventh features (1) to (7), the drive device comprises an electromagnetic drive device which includes an axis member as the output member; an outer tubular member which is spaced outward from the axis member in a direction perpendicular to the axis member; and an electromagnetic force generating device which generates, upon application of an electric power thereto, an electromagnetic force for moving the axis member relative to the outer tubular member in an axial direction parallel to the axis member, and the second biasing device comprises at least one annular leaf spring which is provided between the axis member and the outer tubular member, such that an inner peripheral portion of the annular leaf spring is fixed to the axis member and an outer peripheral portion thereof is fixed to the outer tubular member, so that the annular leaf spring positions the axis member relative to the outer tubular member in the direction perpendicular to the axis member while allowing the axis member to be moved relative to the outer tubular member in the axial direction.
In the present damping device, the second biasing device is provided by the annular leaf spring which functions as a positioning device for positioning the output member of the drive device. Accordingly, the total number of parts of the damping device can be decreased, and the damping device can be simply constructed and easily manufactured.